How to run a stream based command in place on a file
rtb27 at cam.ac.uk
Mon Oct 18 05:35:42 PDT 2004
I want to run stream based commands like `sed` and `tr` on the contents of a
file, and save the results to the same file.
Obviously I can do this with a temporary file:
$sed s/dog/cat/ myanimals.txt > tmp.txt
$mv tmp.txt myanimals.txt
But is there any way I can do this with a single command?
My first guess would be a "buffer" command that reads a file into memory (or
into a temp file) then pipes it to stdout, e.g.
$cat myanimals.txt | buffer | sed s/dog/cat/ > myanimals.txt
But there isn't one which, in my experience of BSD, means it either wouldn't
work or there is a better way to do it :-)
Having read through the Bash manual and run some experiments, it seems that
the ">" operator truncates an output file to zero length before any commands
So my missing command becomes:
$cat myanimals.txt | sed s/dog/cat | bufferedwrite myanimals.txt
I can't find anything like this anywhere -- any ideas what the "proper" way to
do this is?
Thanks in advance,
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